1. Field of the Invention
The invention relates to web accumulators for accumulating and discharging a reserve portion of a continuous web passing through the accumulator to enable continuous operation of processing stations on either or both sides of the accumulator when the speed of the web moving through the processing stations temporarily varies between the two stations. The invention is particularly useful for handling weak webs, such as sanitary or tissue paper.
2. Description of the Prior Art
In many processing operations involving continuous lengths of web material, there are temporary differences in operating speeds between two adjacent operating stations. For example, in the manufacture of sanitary or tissue paper products, it is common to unwind paper from a large parent roll and conduct it through a finished or converting operation. In such operations, it is often desirable to rewind the paper into rewound rolls of a specific size which are not necessarily the same size as the parent rolls, resulting in either the parent roll being depleted before the rewound roll is completed or the rewound roll being completed before the parent roll is depleted. The operation is then maintained by splicing a new parent roll to the end of the paper or by starting a new rewound roll, either of which would require halting the operation unless a reserve portion of the web had been accumulated for continued operation of the rewound roll or a reserve portion of the web can be accumulated while a new rewound roll is prepared. This problem is quite old and is generally solved through use of web accumulators.
The typical accumulator for such uses is the festooning type, such as that disclosed in U.S. Pat. No. 3,645,463. Festooning type accumulators typically consist of a set of fixed web rolls and a set of movable web rolls which are moved towards and away from the fixed rolls. The web is looped alternately from a roll of the first set to a roll of the second set in consecutive order. The movable set of rolls are typically attached to a single carriage which is moved away from the fixed rolls for accumulating a reserved portion of the web and moved toward the fixed rolls for discharging the accumulated reserve portion of the web. The amount of web which can be accumulated is generally quite large for the size of the apparatus, being equal to twice the movement distance of the carriage times the number of rolls mounted on the carriage. Examples of prior art web accumulators are disclosed in U.S. Pat. Nos. 1,261,056; 3,693,860; 3,698,613; 3,700,157; 3,734,370; 3,743,153; and Re. 27,139.
A number of shortcomings exist in the web accumulators of the prior art, particularly for use with weak webs like sanitary or tissue paper. For example, most employ freely rotatable rolls which obtain their rotational force from the web moving across them. Since the portion of the web passing about each roll will be moving at a different speed than the portions of the web passing about other rolls during accumulating or discharging, the use of the web itself to rotate the rolls has been thought in the past to be the only practicable way to drive the rolls. Many of the prior art accumulators are used for accumulating metal strips and other strong web materials where the strong web materials can be depended upon to rotate the rolls. However, weak webs such as sanitary or tissue paper cannot always be relied upon to drive the rolls since the paper is inclined to break. Another common shortcoming of the typical prior art accumulators is their dependence upon the web material to drive the carriage towards the fixed rolls. Again, weak web materials such as sanitary or tissue paper cannot always be relied upon for transmitting carriage driving forces.
It is therefore an object of the invention to provide a web accumulator in which the web is festooned over rolls and each roll is driven by means separate from the web at the speed of the web in contact with it at all times including when it is accumulating or discharging. It is a further object of the invention to provide a web accumulator in which the web is festooned over rolls and in which one set of rolls is driven towards and away from the other set of rolls by drive means separate from the web in response to any difference in speed between the web entering the accumulator and the web leaving the accumulator. And it is a further object of the invention in its preferred embodiment to provide a web accumulator which accomplishes both of the above objects in a single apparatus.